Critics of Lana Del Rey have turned insults about her into an art form, speculating for example that her pout is down to collagen. Photograph: Nicole Nodland

You can still find traces of Lizzy Grant online. There is a video, dated 8 June 2009, that shows a young, casually dressed blonde woman in a green T-shirt and jeans singing alone on stage at a New York music show called The Variety Box. Grant's voice was strong, but she seemed shy and spoke quietly to the audience to a smattering of applause.

Grant looked like any one of hundreds of young artists trying to make it in the clubs and bars of New York, singing their hearts out in the hope that one day they would be spotted. After all, that's how big names from Bob Dylan to Lady Gaga got their breaks. But success never happened to Lizzy Grant. Her one and only album sank virtually without trace.

However, fame did happen to someone called Lana Del Rey, a 25-year-old sultry, seductive songstress who is the current hottest name in US music and whose debut album is one of the most eagerly awaited events in the industry this year. It comes out on 31 January.

Del Rey's image is nothing like Grant's. The video for her new song, provocatively called Born to Die, is slick and lavishly produced. The short film begins with her posing half-naked with a tattooed, shirtless man in front of the stars and stripes, then shows her sitting on a throne in a figure-hugging white dress flanked by two tigers. By the end of the video, she is covered in blood, wearing only a red bra. It is over-the-top and wildly eccentric.

But that suits Del Rey's sound. Her soaring vocals and melodies, reflecting genres as diverse as hip hop and indie music, have won millions of fans. And Del Rey has quite a story to tell. After first appearing on the internet last year with an apparently home-produced video of a song called Video Games, she became a cult hit. She married her music to a mysterious image, self-styled as a "gangster Nancy Sinatra", that paid homage to 1960s fashions and seedy showbiz glamour. In an interview recently shot poolside at the Chateau Marmont in Los Angeles, Del Rey explained her attraction to the notorious celebrity haunt. "It's a place that has inspired so many of my videos and influenced a lot of my visuals," she said through a mouth now framed by pouting, bee-stung lips.

Of course, Lana Del Rey and Lizzy Grant are the same person.

That revelation has made Grant/Del Rey one of the most controversial figures to emerge in US music for years. Some people feel victims of an immense confidence trick. When Video Games first went viral it became an underground sensation praised for its authentic feel. Del Rey's amazing voice crooned the haunting song against a backdrop of grainy out-takes of home movies and Hollywood scenes. It currently has a staggering 20 million views on YouTube. The follow-up, Blue Jeans, with a similar feel, netted 6 million views. Del Rey's few live gigs suddenly sold out. She won the Next Big Thing prize at the Q awards. She seemed set for the big time. But then questions were asked. A few critics began to wonder if, far from being some organic wunderkind, the transformation from Grant to Del Rey had been planned all along. Her stage name was chosen by her management. Rather than being an outsider struggling for recognition, Del Rey is in fact the daughter of a millionaire father who has backed her career. People were suspicious of the way Grant's failed album, and all her social media websites, appeared to have been scrubbed from the internet just before Del Rey appeared. There has been much speculation as to exactly when Del Rey teamed up with her current label Interscope and how much influence their savvy marketers might have put into her original emergence.

"There are a lot of things that don't seem organic about it," said Steven Horowitz, who wrote a cover story about Del Rey for Billboard magazine. "She's putting on a show. She's here to entertain us."

Suddenly, many of the fans that had boosted Del Rey turned on her in spectacular fashion. Music blogs poured vitriol on her talents. Some influential music websites, such as Hipster Runoff, have turned insulting Del Rey into an art form. Last weekend Del Rey appeared as the musical guest on Saturday Night Live. She gave a hesitant, uncertain performance – suddenly more Lizzy Grant than Del Rey – that triggered brutal criticism.

Celebrities even got in on the act. Actress and musician Juliette Lewis tweeted: "Watching this 'singer' on SNL is like watching a 12-year-old in their bedroom when they're pretending to sing and perform." Even news anchor Brian Williams weighed in, sending an email that was later published on gossip website Gawker that called Del Rey's performance one of the "worst outings in SNL history".

But it is not just Del Rey's music and SNL performance that is being hauled over the coals. It is also her appearance.

Pictures of Lizzy Grant when contrasted to Del Rey have led many to speculate that she has had collagen injections in her lips and perhaps even plastic surgery. It is a charge she vehemently denied in a recent interview. "I haven't had anything done at all… I'm quite pouty. That's just how I look when I sing," she insisted.

Del Rey has many defenders too. "She is just a gorgeous creature," said Noah Levy, senior news editor at In Touch Weekly magazine. Horowitz said that whatever the truth of her emergence there is little doubt about her talent or commitment. "I think she cares about the art that she is creating. I don't think that is fake at all," he said.

Despite the outrage directed at her, Del Rey is employing one of the oldest tricks in the book: the creation of a stage persona. Some of the greatest names have done it. David Bowie and Madonna are notorious shape-shifters. So is Lady Gaga. Changing from Lizzy Grant to Lana Del Rey is not unusual when you consider that Bob Dylan's real name was Robert Zimmerman and Iggy Pop was born James Osterberg. "I think Lana Del Rey is manufactured. But when Lizzy Grant came out with music it failed. So she reinvented herself and it worked," said Levy.

In fact, Lana Del Rey's rise says much about the nature of modern fame in the US. The internet has allowed figures like her to come rapidly to the fore of the cultural landscape, whether or not their emergence is planned by a record executive or happens spontaneously from someone's bedroom. It has speeded up the fame cycle. It is worth noting that the huge backlash to Del Rey is happening before her first album has even been released. This reveals a cultural obsession with the "authenticity" that fans, artists and corporations all prize above all else.

Cultural critics say genuine authenticity is almost impossible to achieve. "The whole idea of authenticity is elusive. It is in many ways a complete illusion," said Professor Robert Thompson, a pop culture expert at Syracuse University. Others have simpler explanations for the stir Del Rey has caused, seeing misogyny against a female artist so willing to use sexuality as a way of selling her music. "There is a 'mean girls' attitude to some of it," said Horowitz.

Either way it does not seem likely that Del Rey will be leaving the music scene any time soon. Sales of her new album are set to be astronomical. It has crept into Amazon's top 25 in the US on pre-sales alone. She is booked for appearances on major talk shows. "Lana Del Rey can go anywhere that she wants to," said Levy. "She's going to one day be the cover of Rolling Stone." Lizzy Grant may have failed to make it. But her next creation seems ready for stardom.